This invention relates to a digitizer for measuring the coordinates of a cursor.
Digitizers use various types of sensing devices, including electromagnetic induction, static electric induction, and untrasonic scanning; resolution varies from 25 m to 200 m, while precision varies from 0.05 mm to 0.2 mm, and sampling speed varies from 20 to 200 points per-second. Each kind of digitizer has its own specification. When precise reading and relatively high precision are required the electromagnetic type is recommended. Normally, the electromagnetic type digitizer uses a.c. of about 100 KHz to drive a cursor and to generate alternating magnetic fields in sense lines arranged in the form of lattices. Voltages developed in the sense lines are used to determine the center of the cursor.
Some electromagnetic type digitizers use phase differences to determine the center position of the cursor, phase of the signal on the right side of the cursor being opposite to that on the left side. Amplitude of a cursor position signal is sensed to develop a zero-crossing point; the zero-crossing point is used as a basis for determining the center position of the cursor.